Systems and EIS Quality Indicators

Electrochemical systems are often nonlinear and time-variant—conditions that can distort impedance measurements. This white paper introduces two quantitative quality indicators: Total Harmonic Distortion (THD) and Non-Stationary Distortion (NSD). These metrics help determine whether a system is suitable for EIS and identify errors caused by nonlinearity or transient behavior. Through simulations and examples, the paper illustrates how THD and NSD behave across system types— depending on their linearity and stationarity simultaneously. These indicators provide an objective way to assess measurement quality and support the interpretation of complex electrochemical processes. Ideal for researchers seeking reliable EIS data analysis and documentation.